"Rapid exchange"-type balloon dilatation catheters are catheters which are capable of advancement into the vascular system of a patient along a preemplaced guiding catheter or guidewire, for balloon angioplasty or the like. Typically in a rapid exchange catheter, the guidewire occupies a lumen of the catheter in only a distal portion thereof. With respect to the catheter proximal portion, the guidewire typically exits from the internal catheter lumen through a hole or slit, and extends along the side of the catheter, being typically retained in that position by a guiding catheter in which both the catheter and the guidewire are contained. Examples of rapid exchange catheters include those disclosed in Horzewski, et al. U.S. Pat. No. 4,748,982, Bonzel U.S. Pat. No. 4,762,129, Yock U.S. Pat. No. 5,040,548, and Johnson U.S. Pat. No. 5,205,822.
A chief advantage of rapid exchange catheters lies in the fact that they can be removed from an advanced position in the vascular system of a patient, being withdrawn along the guidewire without inadvertently causing the guidewire to withdraw as well. Thus there is no need for a guidewire extension, which is attached to the proximal end of the guidewire to give the guidewire more length.
As another technique and device for rapid exchange catheters, Teirstein, et al. U.S. Pat. No. 5,234,407 discloses the use of an "exchange catheter" which is inserted between the guidewire and the balloon dilatation catheter before the balloon dilatation catheter is withdrawn. The guidewire extends alongside such a catheter, passing through a pair of apertures in the exchange catheter. This can serve in proper circumstances to prevent the inadvertent withdrawal of the guidewire as the balloon dilatation catheter is withdrawn.
However, there are disadvantages involved in having the guidewire occupy a position alongside rather than inside of a proximal portion of the catheter.
In accordance with this invention, another approach is provided for imparting a rapid exchange capability to a balloon dilatation catheter carried on a guidewire, without the need for a guidewire extension unit and without the need for a portion of the guidewire to pass through the catheter wall and reside outside of a proximal portion of the catheter. Thus the steering of the catheter of this invention can be improved. Also, the guidewire lumen of such a catheter can be pressurized for desired fluid flow without the risk of side leakage through any aperture, slit, or frangible area in the catheter wall.